Silly idiot ran trams — in this capacity? (13)
I believe the answer is:
administrator
'this capacity?' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'silly idiot ran trams' is the wordplay.
'silly' indicates an anagram.
'idiot'+'ran'+'trams'='idiotrantrams'
'idiotrantrams' is an anagram of 'ADMINISTRATOR'.
'in' is the link.
(Other definitions for administrator that I've seen before include "Official organiser" , "Business organiser" , "One managing business affairs" , "Executive" , "Runner" .)